the incumbent fighting to hold onto his seat is democrat jon tester. and he says he's not happy about all this outside money. >> we're going to see a ton of money spent in montana. we're seeing money earlier, more of it, and with more regularity. and i think we're in the process right now of building a campaign infrastructure that's going to be very difficult to pull down as time goes on. it's getting to be big, big, big money. >> ryssdal: big money is at the heart of this story. two years ago, the supreme court changed the landscape of campaign finance with a controversial decision in a case called citizens united. it let corporations and unions spend unlimited amounts of money in campaigns. but to avoid corruption, the court said the money can't go directly to candidates. it has to go to independent outside groups. the key word here being independent. one supporter of citizens united is tester's opponent. >> see y'all later. >> ryssdal: six-term republican congressman denny rehberg. >> you dropped it. train come through, you're dead. if you believe i